Carbide tipped gauge block



Jan. 9, 1951 D. c. FONDA 2,537,340

CARBIDE TIPPED GAUGE BLOCK Filed Sept. 28, 1945 INVENTOR ATTORNEY Patented Jan. 9, 1951 UNITED STATES PATENT OFFICE CARBIDE TIPPED GAUGE BLOCK Douglass C. Fonda, Stamford, Conn.

Application September 28, 1945, Serial No. 619,197

v Claims. 1

This invention relates to gage 'blocksand more particularly to gage blocks tipped with tungsten carbide for increasing the 'usefullife of the blocks by making them more resistant to wear.

It is an object of this invention to provide an improved steel gage block tipped with tungsten carbide and constructed in such a way that the block will 'not lose its flatness as a result of the different coefficients of expansion of the steel and tungsten carbide. Another object is to provide a method of making such blocks.

One feature of the invention relates to the fastening of the carbide tips to the intermediate steel portion of the block by fastening means that hold the tips firmly against the steel portion but allow limited shifting of the contacting steel and tungsten carbide surfaces over one another. It is this feature that makes it possible for the tips and body of the block to expand at different rates, with change of temperature, with- .out affecting the flatness of the gaging surfaces.

Without this feature, differential expansion would either warp the block in the way that a bimetal thermostat warps, or would set up stresses which would ultimately impair the accuracy of the gage'block.

Another object of the invention is to provide an improved method for making composite gage blocks of extreme accuracy. This object is attained by forming the carbide tips for cooperation with the fastening means, by lapping those surfaces of the component parts which are to be brought together in the assembled block, then fastening the parts together, after which the gaging surfaces, and in some cases the fastening elements, are lapped to bring the block to its final dimensions.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views,

to the labor and time required to make a gage block.

At either end of the intermediate body portion 10 th'ereis a tungsten carbide tip H which is of the same cross section as the body portion 10 and secured to the body portion by fastening means, preferably screws Q2. The tips II are made of tungsten carbide and the openings for the screws are preferably formed in the tips during the sintering operation by which the tips are made. .Carbide tips of at least /4 inch thickness give the best results. Thinner tips sometimes warp.

The openings in the tips 5 l for receiving screws [2 have countersunk upper ends into which the heads of the screws extend, and the lower portions of these openings are slightly larger than the outside diameter of the threads of the screws I2. The heads of the screws are preferably cylindrical and of slightly smaller diameter than the counter-sunk portions of the openings into which they extend. Experience has shown that a running clearance of approximately 0.0005

inch around the heads and threads of the screw !2 i sufficient to permit a limited movement of the tip ll over the face of the body portion it with which it contacts. A running clearance is a clearance suf icient to permit a part to move freely with respect to an adjacent surface of another part. v

The shoulder at the bottom of the head of the screw l2 clamps the tip it firmly against the body portion 18 of the block, but the clearance body portion ill have been lapped. Before assembly of the parts, the end faces of the body portion 5!] are lapped to about a class B finish.

Before assembly, the openings and countersinking of tips II are cleaned out with a cylindrical lap charged with diamond dust. The bottom face of the upper tip I I, and the top face of the lower tip II are lapped, and the tips are then assembled with the body portion II in the manner illustrated in Figure 2. The parts are of such dimensions that the total height of the composite block at the time of assembly measures approximately 15 to 20 thousandths of an inch more than the desired dimension of the block between the gaging surfaces.

In the illustrated construction the screws 12 originally have heads in which there are slots I 6, and the slotted portion of the screw heads are above the face of the tip H. After assembly of the tips and body portion, the blocks are beveled by just breaking the corners, the slotted portions of the screws 12 are ground 01f flush with the surface of the block tip, and the composite block is then lapped to final size. Other types of screws can be used, including screws having slotted heads, or other tool-receiving recesses, below the gaging surfaces of the bloclc The blocks can be made with screw heads that are slightly lower than the gaging surfaces, and this does not interfere with the accuracy of the blocks in use because of the measurements taken across the entire face of the block.

I claim as my invention:

1. A gage block including a metal body portion having smooth upper and lower end faces, tips made of material harder than the body portion of the block and each having a different coefficream: expansion from the body portion and overlying both the upper and lower end faces of the body portion, each of said tips having a smooth inner face that contacts with an end face ofthe body portion, and each of said tips ,having an outer face that comprises one of the gaging surfaces of the block, a plurality of screws extending through transversely spaced openings in each of the tips and through said upper and lower end faces of the body portion and thread- ,ing into the body portion of the gage block, at

least one of said screws through each tip having an enlarged part that bears against an inside surface of the opening in the tip and by pressure against said inside surface clamps the tip firmly against the end face of the body portion witha Ilimited clamping force, the opening through the tip having some clearance around the screw that has the enlarged part so that the limited clamping force and clearance leave the confronting surfaces of the body portion and tip free toislide on one another transversely of the gaging dimensionof the block in response to thermal expansions and contractions of said block. T

2. The gage .block described in claim 1 with the metal body portion of the block of unhardened each of the tips to the body portion of the block, isaid fastening means including at least two fastening elements extending through substantially aligned openings in the confronting faces of the tip and block and holding the tip and body portion in a predetermined relation to one another with the tip clamped against the end face of the body portion with a limited clamping pressure that prevents relative movement of the tip and body portion in the direction of the gaging dimension of the block, at least one of the fastening elements for each tip having clearance around it for a portion of its length correlated with the coefficients of expansion of the tip and body portion and suflicient to provide for relative movement of the tip antibody portion transversely of the gaging dimension of the block during thermal expansion and contraction of the block within its intended range of operating tem perature.

4. The gage block described in claim 3 and in which the body portion of the block is made of unhardened steel, and the tips are made of tungsten carbide.

5. Agage block comprising an unhardened steel prism of rectangular transverse cross-section and with side walls and upper and lower end faces, two tungsten carbide tips of substantially less height than the steel prism but of the same transverse cross-section aS the steel prism and having side Walls that form flush continuatio'ns of the side walls 'of'the prism, each of the tips having a lapped face in contact with a lapped face of the prism and having two openings therethrough on different sides of the center of the end faces of the tip and'having a counter-bore that forms a shoulder intermediate the upper and lower ends of the opening, said shoulder lying in a plane substantially normal to the axis of the opening, screws extending through theopenings in the tips and threading into openings in the end faces of the prism, each of said screws having a head that provides an annular shoulder with a surface in a plane normal to the axis of the screw and in contact with the surface of the shoulder formed by the counter-bore, said screws comprising permanent, non-adjustable connections between the tips and the prism and having the upper ends of their heads plane and said screws comprising continuous surfaces flush with the gaging surfaces of the carbide tips and the screws having clearance in the openings through the tips to allow for the different thermal expansion of the steel prism and carbide tips.v

DoUGLA ss c. FONDA.

' REFERENCES CITED 4 The followingreferences are of record in th file of this patent: I

UNITED STATES PATENTS 

